This invention is concerned with a brush device for a miniature electric motor.
It has so far been a general practice that the brush device for the miniature electric motors is made as simple a construction as possible by causing the brush made by powder-forming on a leaf spring of beryllium-copper alloy having a thickness of 0.15 mm or so, for example, to be held on the commutator portion of the motor, thereby utilizing the leaf spring as a brush holder, an electrically conductive body, and a contact-pressure holding body.
In the brush device of the above-described construction, the brush per se is made of such materials having a high metal content, and also it is made of such other materials having a high graphite content. When the metal-graphite brush of high metal content is to be mounted on the leaf spring, it is done in such a manner that a head part of the brush in a rectangular form is fitted into a hole or opening perforated in the leaf spring serving as a brush holder, and the rectangular head part of the brush protruded from the perforated hole or opening in the brush holder made of the leaf spring is caulked so as to fixedly secure the brush to the brush holder. In this case, an electrically conductive adhesive agent may also be applied to the caulked part of the brush as an additional reinforcing expedient to ensure rigid fixation of the brush to the leaf spring holder.
On the other hand, when the metal-graphite brush of high graphite content is to be mounted on the brush holder made of the leaf spring, the afore-mentioned caulking expedient cannot be adopted, because the brush per se is very brittle. In this case, therefore, the brush is mounted on the brush holder in such a manner that a resilient lining member is first fitted onto and along a pair of opposing sides of the opening perforated in the leaf spring holder, and then the rectangular head part of the brush is intromitted into the opening, and, while holding the brush by the abovementioned resilient lining member, an electrically conductive adhesive agent is applied to the fitted part between the brush and the perforated opening, to which the brush contacts, thereby fixedly securing the brush to the leaf spring holder. It goes without saying that this reinforcing expedient may be applied to the first-mentioned case where the brush to be mounted on the leaf spring holder is made of the material of high metal content.
The brush device manufactured in accordance with the abovementioned conventional technique, however, has been replete with various problems mainly in respect of its industrialized mass-production, hence expected reduction in cost of manufacture of the miniature electric motor for controlling purposes in various kinds of automatically operated apparatuses and appliances, the demand for which in the market has been, and is, extremely high, cannot be realized. The source of such problem resides in its necessity for considerable number of manufacturing steps in assembling the brush and the leaf spring holder by caulking as well as in mounting the resilient lining member on the leaf spring holder.